The amateur or professional cabinet maker is faced with the decision of how best to join separate pieces of wood when designing and building various pieces of furniture and or structures. The joints may be such that the edges of the adjoining boards meet at right angles and the face planes of the boards are perpendicular, such as a drawer or chest. The edges may also be parallel to each other with the two board members in the same plane, such as the face frame of a cabinet. The selection of the joint ultimately used becomes one of considering the required strength, appearance and size of the structure and the capabilities of the individual cabinet maker.
There are a large variety of such joints all of which are ordinarily glued and do not use mechanical fasteners, i.e. screws or nails. To increase the strength of the joint, various configurations are cut either parallel to or across the edge of the boards to be joined. The joint configuration may separately or in combination utilize the following principles:
1. Increase the surface area for glueing. The most simple example is a mitered joint where the edges are cut at 45 degrees and the surface area is increased by 41%. The strength of this joint is solely dependent on the glue characteristics.
2. Utilize concealed supports within the joint such as dowels, splines, biscuits, or a mortice and tenon as shown in FIG. 8D, which provide additional glueing surface area and some additional strength from the concealed supports.
3. The surface area for glueing is increased and the mechanical configuration of the joint provides further support for anticipated loads. The box joint, FIG. 8B, is an example of such a joint.
4. The joint is configured such that it can be assembled only in one direction. The loads on the structure in the perpendicular direction are carried by the wedging action of the wood making it a still stronger joint. Typical of such a joint are 1) the half blind dovetail joints commonly used to assemble drawers and 2) the through dovetail joint, FIG. 8A, which is most commonly used in building large chests.
Adding to the flexibility and diversity required of the jointer are the range of physical dimensions of the piece, the wood thickness, width and length of the member as well as the various configurations and sizes of bits which are available.
This invention describes a method and apparatus for forming the matching joints in materials such as wood. More particularly the configured templates can form a majority of the joints normally employed. It is especially useful for completing large structures which are too bulky to be set up on a table saw or on a router table. The jointer in this case is firmly fastened to the member(s) to be cut which in turn are held in position in a bench vice, etc. The principles disclosed for configuring the device can as well be applied to a smaller structure and/or router table/table saw application.
Two joints typical of the above discussed features are the box joint shown in FIG. 8B, and the through dovetail joint shown in FIG. 8A. In order to understand the functional requirements imposed on the jointer it is necessary to describe in more precise detail the geometry and symmetry of the joints. The box joint FIG. 8B can be best described as a regular pattern of identical Square tooth cuts, the center lines of which are displaced on the joining members 206 and 207 by the width of a cut or tooth. The joint can be assembled through from either direction by inserting either member into the other. The uncut portions of both edges 208 and 209 are visible and hence it is a through joint. This joint requires only a straight router bit for completion.
The through dovetail joint of FIG. 8A has two very differently shaped edges, formed of a tail member 201 and pin member 204. On the tail member 201 a dovetail shaped cutout 202 is made perpendicular to and through the face of the member. The remaining section between the cuts is defined herein as a tail piece 203. On the pin member 204 the integral pins 205 are cut on the edge. When viewed from the ends the pins 205 have the exact shape of the dovetail cutouts 202 in the tail member 201.
This joint can only be assembled in one direction by inserting the pins 205 respectively into the dovetail cutouts 202. In the perpendicular direction the boards are restrained by the wedging action of the pins 202 in the dovetail cutouts 205. When glued this is an exceptionally strong joint and has been utilized by early craftsmen prior to the advent of power tools. This joint can be hand cut and is most attractive when assembled. Because of these features it is highly desirable to utilize a jointer together with a power tool to fashion the joint. Because of the seemingly irregular and complex shapes the jointer must complete a series of operations. Because of the joint geometry two different router bits, a dovetail and straight bit, must be used.
At first observation the through dovetail joint geometry shown in FIG. 8A seems complex. However, on closer examination it is readily understandable and can be translated into more specific geometric and mathematical forms as follows:
1. Material removed from one edge, whatever the shape, must be exactly reproduced at the corresponding location in the matching piece.
2. The corollary is also required, material left on one member must be matched by material removed on the matching piece.
3. The depth of cut in either piece must be equal to or slightly greater than the thickness of the matching piece. If the cut is less than the thickness the edge will not be flush with the face of the matching piece.
4. The centerlines CL 1 and CL2 of the dovetail cutout 202 in the tail member 201 must coincide exactly with the respective centerlines CL 3 and CL 4 of the pins 205 on the pin member 204.
5. The controlling dimensions of the dovetail router bit are the maximum diameter and the slope of the cut and these are the controlling dimensions of the cutouts 202. The dimension at the top of the cut is a function of the depth of the cut.
6. The maximum width of each pin 205 is therefore equal to the maximum diameter of the router bit and the sides of the pins 205 are each cut at an angle equal to the slope of the router bit.
The jointer 10 described in this invention can accomplish the above requirements. The jointer 10 can be positioned, i.e. indexed, relative to a reference edge on the particular workpiece, e.g. tail member 201 and pin member 204, and can accurately locate the centerline, of dovetail cuts and pin locations thereon. The jointer 10 can be firmly held at these positions and indexed to each workpiece and with a series of removable templates attached to the jointer 10 for making appropriate cuts, as will be described, one can accurately make the dovetail cuts and pin geometries. Correspondingly, the jointer can be used to remove the required material in a precise manner between the adjoining pin locations. Because of the flexibility and features incorporated in this invention it is possible to utilize a multiplicity of router bit sizes and shapes with the same or alternate templates. The use of removable templates with the jointer 10 permits a variety of shapes and hence a variety of matching joints to be fabricated.
There are currently two prior art devices to form through dovetail joints, the LEIGH and KELLER jigs which are identified respectively in U.S. Pat. Nos. 4,428,408 and 4,168,730. The LEIGH jig is a device where the templates for both the pin and tail cuts are formed by the front and back sections of a series of moveable guide fingers which when held in position then match the dovetail cut and pin centerlines and form the slope of the pin. Flexibility is provided as to the pin spacing but, because of the shape/slope of the templates, only one dovetail bit can be used. Because of the flexibility of the guide finger arrangement other joints can be made as long as the joint member is within the reach of the device. The KELLER jig can only be used for through dovetail joints and is simply two long metal templates accurately machined to make either half of one specific fixed joint i.e. pin spacing and bit configuration. The reach of both devices is limited to the overall length of the template or guide finger section. With both of these jigs a dovetail bit is used to make the tail member and a straight bit is used for the pin member.
The jointer described in this invention is based on a completely different principle. The cabinetmaker is able to accurately move, i.e. index, the jointer relative to the workpiece, such as members 201 and 204 of FIG. 8A, in reproducible, integral or incremental lengths. A short, removable template (s) is inserted in the jointer which establishes the cut(s) to be made and guides the hand held router. The accuracy is primarily established by the method used to position the jointer which can be positioned, i.e. indexed, in increments of different bit diameters. The flexibility to form different dovetail patterns is accomplished by the ability of the jointer to be accurately and reproducibly positioned on the workpieces. The removable templates permit a variety of shapes to be completed. The reach of the jointer is approximately twice its overall length. The dovetail bit is utilized to form the tail member and to remove the majority of the wastage between the pins which are then completed with a straight bit.